Where did you read the novel?
It's on Violet Lily Translation website! The title is the same so u can look it up easy enough, it still updating too I check their shop and look like it didn't finish yet, so unfortunately need to wait
What chapter in the novel does he get his memories back?
He remembers it little by little (starting from the moment he help the sick Hemoculi by draining their mana at the mining area), but fully remember it is when he become the King of the Hemoculi, which is around chapter 29, can't pin point specifically, but I recommend you read the whole Gray Wall arc anyway (start from chapter 28) because that is peak Eve and Mikael bonding! And if you like smut the rainy day season also a must
Honestly or u can start from chapter 21(5) and it should continue from where the Manhwa left off ahahaha
Mikael after his memories come back is hella cute but there's just something fresh about Mikael before he got his memories back ahahahahaha although I def like the post memories back because it less frustrating.... Anyway! Cute!